1. Field of the Invention
This invention relates to a particle analyzing apparatus, for example, a so-called flow sightmeter in which particles to be examined are passed to a flow cell unit and light is applied to the passing particles to be examined and scattered light and fluorescence emitted from the particles to be examined are photometered, whereby analysis of the particles to be examined is effected.
2. Related Background Art
A flow sightmeter is an apparatus in which sample liquid which is a cell-suspended solution and sheath liquid outside thereof (for example, physiological saline solution) flow at a high speed with a predetermined pressure difference imparted thereto, the flow thereof is hydrodynamically converged, a laser light is applied to particles to be examined flowing to the converged position one by one, and scattered light and fluorescence from the particles to be examined are detected by a photodetector to thereby analyze the property, structure, etc. of the particles to be examined. Such an apparatus is used in the fields of cytology, blood science, immunology, genetics, etc.
The sample liquid and the sheath liquid are stored in discrete containers, and the air in the containers is pressurized by a pressurizing system such as a compressor or a nitrogen gas bomb and each liquid is directed to a flow cell which is a portion to be examined. At this time, the sample liquid is wrapped, or surrounded, in the sheath liquid and is hydrodynamically converged, and the particles to be examined in the sample liquid form in line one by one and pass through the flow cell unit. The flow diameter of the sample liquid is regulated with the particle diameter of the particles to be examined and the measurement speed taken into account, and this regulation is accomplished by regulating the pressure of the air pressurized in the containers in which the sheath liquid and the sample liquid are contained, respectively.
However, there arises the problem that the flow diameter of the sample liquid changes in spite of the pressure of the air pressurized in the containers in which the sheath liquid and the sample liquid are contained being set once.
A first cause of this problem is that as measurement is started, the liquids are consumed and the liquid levels thereof lower, whereby the pressures of the liquids directed to the flow cell are reduced. Particularly, unlike the sample liquid which is interchanged during each measurement, the consumption of the sheath liquid which is used in each measurement is great. U.S. Pat. No. 4,503,385 tries to solve this problem by providing a storing portion and a preliminary chamber for the sheath liquid and keeping the liquid level of the sheath liquid constant, but the apparatus of this patent is somewhat complex in structure and has a problem in stability.
A second cause is that where a filter (particularly for the sheath liquid) for removing impurities is used in the flow path leading from the container to the flow cell, this filter becomes gradually clogged each time measurement is repeated and the pressure loss resulting from such clogging reduces the pressure of the liquid directed from the filter to the flow cell.